2 



$ 



$ 



mm. 



mm. 



mm. 



1.30 



.82 



.61 



.80 



.40 



.27 



.42 



.35 



.28 



.50 



.41 



.31 



1.05 



— 



.50 



384 Wisconsin Academy of Sciences, Arts and Letters. 



DESCRIPTION OF FEMALE. 



Length up to 1.8 mm. but usually smaller. 

 Measurements of average specimens. 



Length 



Height - 



Antennule - 



Abdominal setae 



Longest spine on carapace 



The head is in some cases marked off from the body by a slight depres- 

 sion, not seen in young specimens, and often absent in older individuals. 

 The anterior outline of the head as seen from the side forms a straight 

 or slightly convex line from the attachment of the antennules to the eye, 

 where it passes by an abrupt curve into the dorsal margin. This mar- 

 gin is frequently continuous to the hinder end of the valves, and is 

 nearly straight in young specimens but strongly convex in old females. 

 Ventrally the anterior margin of the head terminates in a small pro- 

 jection to which the antennules are attached. The ventral margin is 

 continued into the labrum, and is entirely devoid of the leaf -like expan- 

 sion characteristic of Latona, Sars' organum affixionis. Above the inser- 

 tion of the antennae the valves are continued into small bilobed f ornices, 

 resembling those of Latona but much smaller, and not continued to the 

 insertion of the antennules as are those of Latona. The head as seen 

 from above is somewhat pyramidal in form. 



The carapace does not differ greatly from that of the Sididce in gen- 

 eral. It leaves the oral structures uncovered in front; it is straight or 

 convex dorsally according to the age of the animal; the ventral margin 

 is evenly rounded and passes into the nearly straight posterior margin 

 by a curve which forms no marked projection. The upper posteal angle 

 is well marked. The edge of the carapace is fringed with long plumose 

 setae, each set on a small elevation. At the lower posteal angle are placed 

 three setae, much longer than the others. They are often longer than 

 the carapace, and diverge from each other as they leave the shell, one 

 passing nearly straight backward and the others more outward. These 

 setae are longer in our species than in L. australis as figured by Sars. 

 The valves are not marked except by the braces (Stutzbalken). 



Along the inside of the hinder edge of the shell, from the insertion of 

 the long setae to the junction of the valves, runs a row of fine ' spines 

 like those of Latona. 



APPENDAGES. 



The antennule consists of the basal part, the sense-hairs and the flagel- 

 lum. The first is short, oblong, freely movable. The sense-hairs num- 



